The invention relates to a method for determining a rotational speed of a rotating driveshaft of an internal combustion engine. Proceeding from a rotating driveshaft with a macroscopically reducing angular speed, the rotational speed of the driveshaft, for example of the crankshaft, should be determined at a later point in time (prognosis of the rotational speed or of the rotational speed course). Here, a macroscopically reducing angular speed is understood to mean, by way of example, the property that a rotational speed changes in a manner which can be detected by a human. Such a situation is present, for example, when the internal combustion engine is shut down and, by way of example, passes from the idle state to the standstill state.
DE 10 2006 011 644 A1 discloses an apparatus and a method for operating an apparatus having a starter pinion and a toothed ring of an internal combustion engine. In this case, the rotational speed of the toothed ring and of the starter pinion is determined in order to engage the starter pinion, after the internal combustion engine has been shut down, at a substantially identical rotational speed during the run-down of the internal combustion engine. Values from a characteristic map of a control unit are assigned in order to determine the synchronous engagement rotational speeds.
DE 10 2006 039 112 A1 describes a method for determining the rotational speed of the starter of an internal combustion engine. Said document states that the starter comprises its own starter control unit in order to calculate the rotational speed of the starter and, in start-stop operation, in order to accelerate the pinion of the starter initially without engagement, if self-starting of the internal combustion engine is no longer possible on account of the fact that the rotational speed has dropped. The pinion is meshed at a synchronous rotational speed into the toothed ring of the running-down internal combustion engine.
The German application DE 102008041037 describes how a rotational speed behavior of a crankshaft of an internal combustion engine is prognosticated. In this case, rotational speed or time pairs of past top dead centers or bottom dead centers (relative extrema) are used for forecasting the rotational speed behavior of the crankshaft or of the driveshaft and the point in time for following top dead centers and bottom dead centers.